Method for producing long bagworm silk threads and production device therefor

ABSTRACT

An object of the present invention is to develop a method of producing pure and long bagworm silk threads having no contaminants, such as pieces of leaves and twigs, and a device for implementing the production method. 
     Provided is a method of producing a long bagworm silk thread, the method having a spinning process of making a bagworm having its nest hang its legs on a rail and continuously spin a silk thread along the rail, wherein the rail has a width smaller than the maximum width between the left and right legs when the bagworm used spreads out its legs and wherein the rail is such that the bagworm can hang its legs on the rail, and a collection process of collecting a long silk thread from the rail after the spinning process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/626,815, filed Dec. 26, 2019 which in turn is a 371 ofPCT/JP2017/023839, filed Jun. 29, 2017, the contents of each of whichare incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method of producing a long silkthread derived from a moth larva belonging to the family Psychidae,i.e., a bagworm, a device for producing the same and the like.

BACKGROUND ART

Threads constituting insect cocoons and hairs of mammals have been usedas animal fibers for clothes and the like since long time ago.Especially silk threads from a silk moth (Bombyx mori) larva, namely asilkworm, which are herein often referred to as “silkworm silk threads”,have excellent properties for absorption and desorption of moisture,moisture retention, and heat retention, and also have a unique gloss andsmooth texture. Therefore, the silkworm silk threads are valuable andexpensive natural materials even today.

However, there exist animal fibers in nature having propertiescomparable or superior to those of silkworm silk threads. Recently, forutilizing animal fibers having such excellent properties as novelnatural materials, exploration thereof and research thereon are ongoing.

Threads derived from spiders (herein often referred to as “spiderthread”) is one of such materials of interest. Spider threads haveflexibility and elasticity and have an elastic force up to 5 to 6 timeshigher than that of polystyrene, and are thus expected as a medicalmaterial for surgical suture and the like, and as a special material foremergency ropes, protective clothes, or the like (Non-Patent Literatures1 and 2). However, mass-production of spider threads is not possiblebecause mass rearing of spiders and collecting a large amount of threadsfrom spiders are difficult. Another problem is that the production costis high. Currently, an attempt to overcome these problems is ongoing byusing gene recombination technology to produce spider threads insilkworms or Escherichia coli (Patent Literature 1 and Non-PatentLiterature 2). However, the silkworm or Escherichia coli used for spiderthread production are recombinants and are thus allowed to be reared orcultured only in facilities having defined equipment, whichdisadvantageously involves a large maintenance or management burden.Additionally, spider thread proteins expressed in Escherichia coli arein a liquid state and are needed to be converted to fibers, which alsodisadvantageously increases the number of processes. Furthermore,another disadvantage is that currently spider threads spun by therecombinant silkworms are merely comprised in silkworm silk threads atseveral percentages and cannot be obtained as 100% spider threads whichallow 100% of the properties of spider threads to be utilized.

There exist insects called bagworms (also known as “basket worms”). Thelarvae of moths belonging to the family Psychidae in the orderLepidoptera are collectively referred to as bagworms and are known tospend the whole larval stages living with spindle-shaped orcylinder-shaped nests (bag nests) made of pieces of leaves and twigsassembled by threads (FIG. 1 ), during which the larvae usually hidethemselves inside the nests and move with the nests even for eating.Bagworms are also insects familiar to people from long time ago, and abagworm with its nest hanging from a branch of a bare tree in wintertime is a typical winter scene.

The bagworm-derived threads (herein often referred to as “bagworm silkthreads”) have mechanical properties superior to those of silkworm silkthreads and spider threads. For example, bagworm silk threads fromEumeta minuscula have an elastic modulus up to 3.5 times of that ofsilkworm silk threads and 2.5 times of that of spider threads of Nephilaclavata, and have a very high strength (Non-Patent Literatures 1 and 3).Additionally, a monofiber of bagworm silk threads has a cross-sectionalarea only about one-seventh of that of a monofiber of silkworm silkthreads, which allows production of fine, thin and light fabrics with asmooth texture. Moreover, bagworm silk threads have a gloss and a shinyappearance comparable or superior to those of silkworm silk threads.

Bagworms are more advantageous than silkworms also in terms of rearing.For example, since silkworms feed on only raw leaves of mulberry(species belonging to the genus Morus, including, for example, M.bombycis, M. alba, and M. lhou) in principle, the region for rearing andseason for rearing depend on the supply area of mulberry leaves and theseason of mulberry leaf development. In contrast, bagworms areeuryphagous, the specificity for food leaves is low, and many species ofbagworms can feed on leaves of trees of various species. Accordingly,food leaves for bagworms are easily obtainable and bagworms can beraised in any region. Also, bagworms of some species can feed on leavesof evergreen trees. Thus, differently from mulberries, which aredeciduous trees, it is possible to supply food leaves all year round.Moreover, bagworms are smaller in size than silkworms and require arearing space equal to or less than that required for rearing silkworms,which makes mass rearing easy. Thus, the cost for rearing cansignificantly be reduced compared with that for rearing silkworms.

Also, bagworms are more advantageous than silkworms in terms ofproductivity. For example, silkworms spin a large amount of threads onlyduring cocooning and all larvae perform cocooning in the same period.Thus, a disadvantage of silkworms is that thread collection periodsoverlap and labor periods concentrate thereon. In contrast, bagwormsrepeatedly spin silk threads for nest building or migration throughoutlarval stages. Thus, bagworms have an advantage in that labor periodscan be dispersed by artificially adjusting the thread collectionperiods. Additionally, bagworm silk threads can be directly collectedfrom wild-type bagworms, and thus it is not required to generate ormaintain recombinants as is required in the case of production of spiderthreads.

As described above, bagworm silk threads have properties superior toconventional animal fibers and also have many advantages for theirproduction, and thus can be a very promising novel natural material.

However, in the practical application of bagworm silk threads, there areseveral major problems which are unavoidable and difficult to solve. Themost important problem is that long monofibers cannot be obtained frombagworms. In the case of silkworms, cocooning is carried out bycontinuous spinning, and a long fiber can thus be relatively easilyobtained by cocoon scouring and reeling. In contrast, bagworms pupate intheir nests where the bagworms spend their lives in the larval stage,and therefore do not perform cocooning behavior before pupation.Additionally, since a nest of a bagworm is extended as the bagworm growsfrom the first instar in principle, old and new silk threads are mixedtogether in the nest. In addition, a nest of a bagworm has an opening atone end of the longitudinal axis (FIG. 2A: thick arrow), out of whichthe bagworm exposes its head and a portion of its thorax for migrationand eating, and an outlet for excretion at the other end for excretionof feces and the like. Since a bagworm nest always has two openings,silk threads are fragmented in the nest and are discontinuous. Thus,bagworm nests are by its nature assembled by relatively short silkthreads entangled with each other, and long fibers cannot be obtainedfrom the nests by conventional methods. Furthermore, bagworm nests arecomposed of three layers, i.e., the outermost, intermediate, andinnermost layers, and the outermost and intermediate layers comprise alarge amount of gummy material, which are difficult to completely removeeven if scouring is repeated. By conventional technologies, spinning canbe performed only from the innermost layer, which does not comprisegummy material, but the silk threads less than 50 cm long can be merelyobtained from the innermost layer.

Further, a bagworm spins a foothold silk thread for preventing fall froma branch or the like in a zigzag pattern (arrowhead), as shown in FIG.2A, and hooks its claws on the thread for migration (thin arrow). Thoughthis type of threads may be used as bagworm silk threads, collection ofthe type of threads is difficult because the migration of a bagwormdepends on the bagworm and is difficult to control. Additionally,spinning again at the same place after spinning there produces multiplecrossovers and complicated entanglement of silk threads spun in a zigzagpattern as shown in FIG. 2B, and thus collection of silk threads isdifficult.

For the reason as described above, it has been considered to be almostimpossible to obtain meter-scale bagworm silk threads as monofibers byconventional technologies. Therefore, fabrics interwoven with bagwormsilk threads have not been known so far. In fact, conventional productsusing bagworm silk threads, such as purses or sandals, are merelymanufactured using unwoven fabrics, which are prepared by removingcontaminants, such as pieces of leaves and twigs, from bagworm nests,expanding and then shaping, followed by patching together the resultingproducts in a patchwork manner.

For practical application of the bagworm silk thread, another importantproblem is that pieces of leaves and twigs and the like are inevitablyattached on the surface of bagworm nests. These contaminants have to becompletely removed for commercialization of bagworm silk threads.However, the removing work requires enormous labor and cost, thusresulting in increased production cost. Additionally, complete removalof the contaminants is difficult with existing technologies, which leadsto low quality of final products due to contamination with a smallamount of small pieces of leaves as well as light-brown staining of silkthreads with pigments from the contaminants and so on.

Accordingly, it has been essential to develop a method of producing pureand long bagworm silk threads comprising no contaminants, for practicalapplication of bagworm silk threads as a novel material of biologicalorigin.

CITATION LIST Patent Literature

-   Patent Literature 1: WO2012/165477

Non-Patent Literature

-   Non-Patent Literature 1: Shigeyosi Ohsaki, 2002, Sen′i Gakkaishi    (Sen′i To Kogyo), 58: 74-78.-   Non-Patent Literature 2: Kuwana Y, et al., 2014, PLoS One, DOI:    10.1371/journal.pone.0105325-   Non-Patent Literature 3: Gosline J. M., et al., 1999, 202,    3295-3303.

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to develop a method of producing along bagworm silk thread comprising no contaminants, such as pieces ofleaves and twigs, and a device for implementing the production method.

Solution to Problem

In the course of studying bagworm silk threads to solve theaforementioned problems, the present inventors found that bagworm silkthreads include at least two types of silk threads, i.e., nest silkthread constituting the nest and foothold silk thread serving as afoothold for migration, and these silk threads differs in theirmechanical properties. Foothold silk threads were thicker and strongerthan nest silk threads. Foothold silk threads were also superior to silkthreads from silkworm and threads from Araneus ventricosus in terms ofvalues of elastic modulus, fracture strength, and toughness.Furthermore, it was found that foothold silk threads can be collected aspure bagworm silk threads without contaminants, such as pieces of leavesand twigs, differently from nest silk threads.

As described above, the foothold silk threads are usually spun in azigzag pattern, and collection thereof was difficult. The studies of thepresent inventors led to the development of a method of making a bagwormspin foothold silk threads in a state nearly parallel to a rail byplacing the bagworm on the rail having a specific width. Then, thepresent inventors succeeded in producing meter-scale continuous purebagworm silk threads, which had hitherto been considered impossible, byimplementing a method of spinning based on the aforementioned findings.The present invention has been completed on the basis of the findingsand successful examples, and provides the following.

-   -   (1) A method of making a bagworm spin a long silk thread, the        method comprising a process of making the bagworm having its        nest hang its legs on a rail and continuously spin the thread        along the rail, wherein the rail has a width smaller than the        maximum width between the left and right legs when the bagworm        used spreads out its legs and wherein the rail is such that the        bagworm can hang its legs on the rail.    -   (2) The method according to (1), wherein the rail has a        closed-ring structure or wherein the rail has an open-ring        structure having one or more gaps which the bagworm can cross.    -   (3) The method according to (1) or (2), wherein the rail has an        inclination of 0 to 70 degrees upward or 0 to 70 degrees        downward.    -   (4) The method according to any one of (1) to (3), wherein the        length of the continuously spun silk thread is 1 m or longer.    -   (5) A method of producing a long bagworm silk thread, the method        comprising: a spinning process of making a bagworm having its        nest hang its legs on a rail and continuously spin the thread        along the rail, wherein the rail has a width smaller than the        maximum width between the left and right legs when the bagworm        used spreads out its legs and wherein the rail is such that the        bagworm can hang its legs on the rail; and a collection process        of collecting a long silk thread from the rail after the        spinning process.    -   (6) The method according to (5), further comprising a scouring        process of scouring the long silk thread simultaneously with or        subsequently to the collection process.    -   (7) The method according to (5) or (6), further comprising a        twisting process of twisting the silk threads after the        collection process or the scouring step.    -   (8) The method according to any one of (5) to (7), wherein the        rail has a closed-ring structure or wherein the rail has an        open-ring structure having one or more gaps which the bagworm        can cross.    -   (9) The method according to any one of (6) to (8), wherein the        rail has an inclination of 0 to 70 degrees upward or 0 to 70        degrees downward.    -   (10) The method according to any one of (5) to (9), wherein the        bagworm used is in the last instar.    -   (11) The method according to any one of (5) to (10), wherein the        length of the continuously spun silk thread is 1 m or longer.    -   (12) A bagworm-derived silk thread having a continuous length of        1 m or longer.    -   (13) The silk thread according to (12), wherein the silk thread        is a monofiber.    -   (14) A fabric comprising a silk thread produced by the method of        producing a long bagworm silk threads according to any one        of (5) to (11) or the silk thread according to (12) or (13).    -   (15) A device for producing a long bagworm silk thread, the        device comprising: a rail having a width smaller than the        maximum width between the left and right legs when the bagworm        used spreads out its legs and wherein the rail is such that the        bagworm can hang its legs on the rail.    -   (16) The production device according to (15), wherein the rail        is composed of a material with a smooth surface.    -   (17) The production device according to (15) or (16), wherein        the rail is composed of an edge part of a plate-shaped member.    -   (18) The production device according to any one of (15) to (17),        wherein the rail has a closed-ring structure or wherein the rail        has an open-ring structure having one or more gaps which the        bagworm can cross.    -   (19) The production device according to any one of (15) to (18),        wherein the rail has an inclination of 0 to 70 degrees upward or        0 to 70 degrees downward.

Advantageous Effects of Invention

By the method of making a bagworm spin a long silk thread according tothe present invention, it is possible to make a bagworm spin a longfoothold silk thread.

By the method of producing a long bagworm silk thread according to thepresent invention, a bagworm-derived pure and long foothold silk threadhaving a length of 1 m or longer can be produced.

By the device for producing a long bagworm silk thread according to thepresent invention, the method of producing a long bagworm silk threadcan readily be carried out.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows the appearance of a nest of a bagworm of Eumeta japonica(a Eumeta japonica bagworm). FIG. 1B shows the inside of the nest of aEumeta japonica bagworm, which has been cut and opened along thelongitudinal axis. The worm located in the middle is an Eumeta japonicalarva, i.e., an Eumeta japonica bagworm.

FIG. 2A shows the spinning behavior of an Eumeta japonica bagworm duringmigration. FIG. 2A shows how a bagworm moves while spinning a footholdsilk thread (arrowhead) and hooks its claws on the foothold silk threadspun by the bagworm (thin arrow), and how the nest is open at one end ofthe nest for exposing a part of its body during migration (thick arrow).FIG. 2B shows the state of foothold silk threads when a Eumeta japonicabagworm spins foothold silk threads under normal uncontrolledconditions. FIG. 2B shows how foothold silk threads spun in a zigzagpattern are entangled with each other in a complicated manner.

FIG. 3A shows a scanning electron micrograph of a spun fiber (a footholdsilk thread) of an Eumeta japonica bagworm. FIG. 3B shows a schematic ofa spun fiber in a bagworm silk thread. The fiber has a structure inwhich two flat-shaped monofibers (microfilaments) (301) are joinedside-by-side by a gummy material (not shown) coating the monofibers.

FIG. 4 shows a basic process flow diagram of a method for producing along bagworm silk thread according to the present invention.

FIG. 5A shows a schematic of a rail according to the present invention.This figure shows a rail having a circular cross section. In the figure,L and φ respectively represent the length of the rail in thelongitudinal axis and the cross-sectional diameter of the rail. In thisrail, φ corresponds to the width of the rail. FIG. 5B shows a dorsalview of the head and thorax of a bagworm spreading out the legs to theleft and right at the maximum width. In the figure, FL, ML, and RLrespectively represent front legs, middle legs, and rear legs. Also, W1and W2 represent the maximum widths between the left and right legs whenthe bagworm spreads out its legs, for middle legs and posterior legs,respectively.

FIG. 6 shows how a bagworm hangs its legs on a rail. FIG. 6A shows how abagworm hangs its legs (arrowheads) on a rail (thin arrow) in a sandwichfashion. The shown picture was taken from right above the horizontalrail. The bagworm is moving in the direction indicated by the thickarrow, while hanging on the rail and hanging down therefrom.

FIG. 6B shows how a bagworm hangs its legs (arrowheads) on a rail (thinarrow) as if the bagworm places its shoulder onto the rail. The shownpicture was taken from diagonally above the horizontal rail. The bagwormis moving in the direction indicated by the thick arrow, while hangingon the rail and hanging down from a side surface of the rail.

FIG. 7 shows drawings for describing rails that a bagworm can hang on. Ato F show cross sections of a plate-shaped member (702) and a railpositioned at an edge part thereof (701). A to C show aspects in whichthe rail faces upward, and D to F show aspects in which the rail facesdownward.

FIG. 8 shows an embodiment of a device for producing a long bagworm silkthread according to the present invention. This figure shows a devicefor producing a long bagworm silk thread having a closed-ring rail as anedge part (802) of a plate-shaped member (801).

FIG. 9 shows an embodiment of a device for producing a long bagworm silkthread according to the present invention. This figure shows a devicefor producing a long bagworm silk thread wherein the rail (901) iscomposed of a helical wire member.

FIG. 10 shows an embodiment of a device for producing a long bagwormsilk thread according to the present invention. This figure shows adevice for producing a long bagworm silk thread wherein two closed-ringrails composed of a wire member (1001, 1002) are connected by a singlerail (1003).

FIG. 11 shows drawings for describing the inclination of a rail in adevice for producing a long bagworm silk thread according to the presentinvention. This figure shows the inclination (a and b) of the rail(1101, 1104) to the horizontal plane (h) in a case in which the railfaces upward (A) and in a case in which the rail faces downward (B),respectively, in the example of the device for producing a long bagwormsilk thread comprising the plate-shaped member (1102, 1103) shown inFIG. 8 .

FIG. 12 shows bundles of bagworm silk threads obtained after thecollection process, which are wound around a bobbin (a) or handles ofpaint brushes (b and c) in the method of producing a long bagworm silkthread according to the present invention. Pure and shiny long silkthreads without contaminants were successfully obtained.

FIG. 13 shows magnified views of bagworm silk threads after each processin the method of producing a long bagworm silk thread according to thepresent invention and a fabric made of bagworm silk threads. FIG. 13Ashows a bundle of bagworm silk threads after the collection process.FIG. 13B shows a bundle of bagworm silk threads after the scouringprocess. FIG. 13C shows a bagworm silk thread after the twistingprocess.

FIG. 13D shows a fabric woven with bagworm silk threads after thetwisting process.

DESCRIPTION OF EMBODIMENTS 1. Method of Making a Bagworm Spin a LongSilk Thread 1-1. Overview

The first aspect of the present invention is a method of making abagworm spin a long silk thread. The method of the present inventioncomprises a process of making a bagworm having its nest hang its legs ona rail and continuously spin a thread along the rail, wherein the railhas a specific width and wherein the rail is such that the bagworm canhang its legs on the rail. By the method of the present invention, it ispossible to make a bagworm spontaneously spin meter-scale silk threads,which have hitherto been considered impossible.

1-2. Definition

The terms frequently used herein are defined as described below.

The term “bagworm” collectively refers to a moth larva belonging to thefamily Psychidae in the order Lepidoptera, as described above. Mothsbelonging to the family Psychidae are distributed worldwide and larvae(bagworms) of any species of the moths spend the whole larval stagesliving in nests covered with natural materials, such as pieces of leavesand twigs, which are assembled by silk threads spun by the larvaethemselves. The nests are spindle-shaped, cylinder-shaped, orcone-shaped bag-like nests that can accommodate the whole body of abagworm. Bagworms usually hide themselves inside the nests and alwayscarry the nests even during eating and migration, and in principle, evenpupate inside the nests.

The species, instar, and gender of bagworms used herein are not limited,provided that the bagworms are larvae of a moth species belonging to thefamily Psychidae and that the species makes a nest as described above.For example, the family Psychidae includes the genera Acanthopsyche,Anatolopsyche, Bacotia, Bambalina, Canephora, Chalioides, Dahlica,Diplodoma, Eumeta, Eumasia, Kozhantshikovia, Mahasena, Nipponopsyche,Paranarychia, Proutia, Psyche, Pteroma, Siederia, Striglocyrbasia,Taleporia, Theriodopteryx, Trigonodoma, etc., and bagworms used hereinare a species belonging to any genus. Specific examples of Psychidaespecies include Eumeta japonica, Eumeta minuscula, and Nipponopsychefuscescens. The instar of the larvae may be any instar between the firstinstar and the last instar. However, large bagworms are preferable forthe purpose of obtaining thicker and longer bagworm silk threads. Forexample, among larvae of the same species, larvae in the last instar aremore preferable, and female larvae are more preferable than male larvaebecause females grow larger than males. Additionally, among the familyPsychidae, large species are more preferable. Thus, Eumeta japonica andEumeta minuscula are species that are suitable as the bagworms used inthe present invention.

The term “silk thread” as used herein refers to a proteinous thread froman insect, which is spun by the insect in larval or adult stage for thepurpose of nest building, migration, anchoring, cocooning, prey capture,and the like. When the term “silk thread” is simply recited herein, itmeans bagworm silk thread, unless specifically noted.

The term “bagworm silk thread” as used herein refers to abagworm-derived silk thread. The “bagworm silk thread” hereinencompasses a monofiber, a spun fiber, and fiber assembly.

The term “monofiber” as used herein, which is also referred to asmonofilament, is the smallest filament unit constituting fibercomponents. The monofiber contains a fibroin-like protein as a maincomponent. Bagworm silk threads and silkworm silk threads in naturalstates are usually spun as a bifilament, but do not exist as amonofiber. However, monofibers can be obtained by removing gummymaterial in the scouring process in the second aspect described below.

The term “spun fiber” as used herein refers to an unprocessed silkthread just spun by bagworms, silkworms or the like, or just secreted byspiders. A spun fiber of bagworms is composed of a bifilament, which isa pair of monofibers, as shown in FIG. 3 . This form is based on astructure in which two monofibers spun from the spinnerets located oneach of the left and right sides of a bagworm are joined together by asericin-like gummy material during spinning. When used in conjunctionwith the term “spin” in a phrase such as “a bagworm spun silk thread” or“spin a bagworm silk thread,” the term “silk thread” is intended to meana spun fiber in principle.

The term “fiber assembly” as used herein, which is also referred to asmultifilament, refers to a fiber composed of a plurality of bundles offibers. A fiber assembly refers to a so-called raw silk thread, and isin principle composed of a plurality of monofibers. Herein, however, afiber assembly also includes those composed of a plurality of monofibersand spun fibers, or a plurality of spun fibers. The term “fiberassembly” as used herein can encompass a fiber mixture in which fibersother than bagworm silk threads such as silkworm silk threads and thelike are mixed. However, the term is generally intended herein to mean afiber assembly composed only of bagworm silk threads, unlessspecifically noted. A fiber assembly is twisted through the twistingprocess described in the second aspect below to become a stronger silkthread. Herein, the fiber assembly includes not only twisted fiberassemblies but also non-twisted fiber assemblies showing a soft andsmooth texture.

Bagworm silk threads include foothold silk threads and nest silkthreads, as described above. The “foothold silk thread” refers to a silkthread spun by a bagworm in advance of migration and functions as afoothold for preventing fall from a branch, leaf, or the like duringmigration. A bagworm usually uses the foothold silk thread as a footholdand hooks its claws onto the foothold silk thread to move in thedirection of migration. A bagworm spins foothold silk threads in azigzag pattern, which facilitates the bagworm to hang the left and rightlegs thereon and which also allows the silk thread attachment sites andthe load on the silk thread to be distributed left and right. On theother hand, the “nest thread” refers to a silk thread forming a nest,which is spun to assemble pieces of leaves and twigs or to make aninternal wall of a nest so that its accommodation space becomes acomfortable environment. In principle, foothold silk threads are thickerand also mechanically stronger than nest silk threads.

The term “long” refers to a length longer than the normal length in theart. Herein, the term “long” refers to being longer than the length ofspun silk threads (a length of less than 1 m) obtainable from bagwormsusing conventional technology in particular. Specifically, the term“long” refers to 1 m or longer, or 1.5 m or longer, preferably 2 m orlonger, more preferably 3 m or longer, 4 m or longer, 5 m or longer, 6 mor longer, 7 m or longer, 8 m or longer, 9 m or longer, or 10 m orlonger. The upper limit of the length is not particularly limited, butcorresponds to the length of silk threads that bagworms can continuouslyspin in the method of the present invention, including, for example, 1.5km or shorter, 1 km or shorter, 900 m or shorter, 800 m or shorter, 700m or shorter, 600 m or shorter, 500 m or shorter, 400 m or shorter, 300m or shorter, 200 m or shorter, or 100 m or shorter. The length of aspun fiber of bagworm silk threads is also the length of a monofiberconstituting it, and corresponds to the length of the threadcontinuously spun by a bagworm. Therefore, a longer bagworm silk threadcan be obtained if it is possible to make a bagworm continuously spin athread. Thus, the method of the present invention is also a method ofmaking a bagworm continuously spin a silk thread.

1-3. Method

The method of the present invention comprises a spinning process as anessential process.

The “spinning process” is a process of making a bagworm having its nesthang its legs on a rail and continuously spin a thread along the railunder an active condition of the bagworm. The configuration of the railis described in detail in the “device for producing a long bagworm silkthread” of the third aspect described below, and is thus notspecifically described here.

The term “active condition” as used herein refers to a condition underwhich bagworms can perform activities involving usual movements such asmigration and eating. Such conditions include, for example, temperature,atmospheric pressure, humidity, brightness, and oxygen level, and themost important condition in the present invention is temperature. Sinceinsects are poikilotherms, they suspend activities and enter dormancy asthe air temperature decreases. Thus, among the active conditions in thepresent invention, the lower limit of the suitable air temperature is atemperature at which bagworms do not enter dormancy. The specifictemperature varies depending on the species, and may be generally 10° C.or higher, preferably 12° C. or higher, more preferably 13° C. orhigher, further preferably 14° C. or higher, still more preferably 15°C. or higher. On the other hand, the upper limit of temperature is theupper limit of temperature under which bagworms can survive. In general,the temperature may be 40° C. or lower, preferably 35° C. or lower, morepreferably 30° C. or lower, further preferably 27° C. or lower, stillmore preferably 25° C. or lower. The atmospheric pressure, humidity,brightness, oxygen concentration, and the like may be equal to oraround, for example, those in plains in temperate areas. For example,the atmospheric pressure is around 1 atmosphere, the humidity rangesfrom 30 to 70%, and the brightness is 6 to 18 hours of bright conditionout of 24 hours, and the concentration of oxygen in the atmosphereranges from 15 to 25%.

The bagworm used in this process is a bagworm having its nest. Sincebagworms generally behave with their nests, a bagworm including its nestmay be used in this process. A bagworm removed from its nest becomesrestless and cannot accomplish the object of the present invention, andtherefore is not used. Additionally, the nest may not be intact,provided that the nest can hide almost the whole body of the bagworm.The nest is not necessarily composed of natural materials such as piecesof leaves and twigs and may be created using artificial materials (suchas paper pieces, wood chips, fiber fragments, metal pieces, plasticpieces, and the like).

The term “hang on” generally refers to hooking and holding, but hereinrefers to that a bagworm hangs its legs on a rail to bear the weight ofthe bagworm itself (including the weight of the body and the nest) andto prevent falling from the rail. However, a bagworm may transientlyhang its legs on a foothold silk thread spun by itself in the course ofmigration. A bagworm can freely hang on and release, and it does notmean that the temporarily hung legs are fixed at that position. Thebagworm can freely move on a rail by repeating hanging on and release ofits legs.

The term “leg” as used herein refers to an entire leg or a part of a legof a bagworm. Legs called thoracic legs extend from the thorax of abagworm, as shown in FIG. 5B. The thoracic legs consist of three legs(front, middle, and rear legs) unilaterally, which means three pairs ofleft and right legs, for a total of six legs. Any of the legs may behung on a rail. Further, the number of legs hung on a rail may be any of1 to 6, but is preferably at least two or more for moving on the rail.For example, the legs hung on a rail include any two or more legs out ofthree legs on either the left or right side, specifically front andmiddle legs, front and rear legs, middle and rear legs, and front,middle, and rear legs on the left side. Additionally, the legs hung on arail include at least one or more legs on each of the left and rightsides out of the six legs.

The phrase “make a bagworm hang its legs on a rail” as used hereinrefers to inducing a bagworm to spontaneously hang its legs on a rail,in principle. The phrase can include artificially making a bagworm hangits legs on a rail. However, even if one tries to force a bagworm tohang on a rail by an ordinary method with human hands, the bagwormbecome cautious, and it is not possible to successfully make a bagwormhang on a rail. The method of inducing a bagworm to hang on a rail isnot particularly limited. Examples of the method include a method usinga guidepath. The “guidepath” as used herein refers to a subsidiarywalkway that is capable of inducing a bagworm to move spontaneously tothe rail. The shape of the guidepath is not particularly limited, butexamples of the guidepath include a single rail similar to a rail, or aplane like a wall. Examples of the method of guiding a bagworm to a railusing a guidepath include a method utilizing the nature of bagworms tomove to a higher location. Specifically, once a bagworm is placed at alocation lower than a rail and a guidepath is placed between thelocation where the bagworm is placed and the rail, the bagwormspontaneously goes up the guidepath and reaches the rail. After reachingthe rail, the bagworm will automatically hang its legs on the rail dueto the structure of the rail.

By making a bagworm hang on a rail under active conditions, the bagwormstarts to continuously spin a thread while spontaneously moving alongthe rail. The phrase “continuously spin a thread” as used herein refersto spinning a thread without interruption. Once the silk thread spewedfrom the left and right spinnerets located on the mouth of a larvabreaks, the continuity is lost.

The direction in which a bagworm moves on a rail can be controlled tosome extent by the shape or inclination of the rail. For example, whenthe inclination of a rail is 0 degree, i.e. horizontal, a bagwormcontinues to move on the rail in the same direction as the direction inwhich the bagworm initially started moving. Specifically, once a bagwormhanging on a circular and horizontal rail starts moving in a clockwisedirection, the bagworm keeps the clockwise direction in principle. Onthe other hand, bagworms have a nature to move to a higher location fromthe current position, as described above. Therefore, when a rail is nothorizontal but is inclined, a bagworm moves along the rail towards thedirection of a higher location by making the bagworm hang on at thelowest position of the rail. By utilizing these characteristics, it ispossible to make a bagworm on a rail move in a desired direction.

As described above, a bagworm essentially spins a foothold thread in azigzag pattern towards the direction of movement during migration.However, by the method of the present invention, a bagworm spins afoothold silk thread nearly in parallel with a rail. This is based onthe structure of a rail and the nature of a bagworm. The rail used inthe method of the present invention is such that a bagworm can hang itslegs on the rail, and the rail has a specific width, which is describedin detail in the third aspect. When a bagworm moves on a rail havingsuch a structure, it is difficult for the bagworm to spin a footholdsilk thread in a zigzag pattern, and the bagworm spins a thread nearlyin parallel with the rail. The foothold silk thread spun in parallelcannot have strength sufficient to bear the weight of the bagworm itselfand appropriate process size intervals. In this case, however, thebagworm can move by hanging its legs on the rail itself. Thus, it isthought that the foothold silk thread spun according to the method ofthe present invention is spun as an instinctive behavior associated withthe migration behavior, without achieving the original function as afoothold for migration. The method of the present invention utilizesthis feature.

The bagworm used in this process may be an individual collected in thefield or an individual bred in successive generations under artificialconditions. In either case, an individual which is not starved ispreferable, and an individual which is fed sufficient amount of foodbefore use is more preferable. An individual which is not starved and isfed sufficient amount of food continues to move on a rail and spin athread for a period from 1 hour to 4 days, from 3 hours to 3 days, orfrom 6 hours to 2 days, under the conditions described above. To make abagworm continue to spin a thread, the structure of a rail is preferablya closed-ring structure having no terminal, i.e., having no end, or anopen-ring structure having one or more gaps which the bagworm used caneasily cross.

By the method of the present invention, foothold silk threads ofbagworms having a continuous length of 1 m or longer can be obtained.

1-4. Effect

By the method of making a bagworm spin a long silk thread according tothe present invention, it is possible to make a bagworm continuouslyspin a thread. This method allows for mass production of long bagwormsilk threads at a practical application level, which are strongerfoothold silk threads, although the production thereof has hitherto beenconsidered impossible.

2. Method of Producing Long Bagworm Silk Threads 2-1. Overview

The second aspect of the present invention is a method of producing longbagworm silk threads. According to the production method of the presentinvention, which has conventionally been difficult, abundant productionof long bagworm foothold silk threads can be easily and stably obtained.The production method of the present invention can be implemented, forexample, using an apparatus for producing long bagworm silk thread ofthe third aspect.

2-2. Method

The flow of the production method of the present invention is shown inFIG. 4 . The production method of the present invention comprises thespinning process (S401) and the collection process (S402) as essentialprocesses. The method also comprises the scouring process (S403) and/orthe twisting process (S404) as optional processes. Though FIG. 4 showsthe basic flow consisting of the collection process (S402) followed bythe scouring process (S403) and the subsequent twisting process (S404),the optional processes are not limited by the basic flow. For example,the scouring process (S403) and the collection process (S402) may beconducted simultaneously, as described below, or the twisting process(S404) may be conducted after the process (S402) and before the scouringprocess (S403). Each of the processes will be specifically describedbelow.

(1) Spinning Process (S401)

The “spinning process” is a process that a bagworm with the nest thereofis made to continuously spin a thread along a rail under the activeconditions, wherein the legs of the bagworm are held on the rail havinga specific width and being capable of holding the legs of the bagwormused.

The details of this process follow those of the spinning process in themethod of making a bagworm spin a long silk thread of the longer.

(2) Collection Process (S402)

The “collection process” is a process of collecting long bagworm silkthreads from a rail, from which a bagworm has been recovered or removedafter the spinning process. In this process, foothold silk threadsobtained from bagworms are spun fibers adhered to the rail by means of asericin-like gummy material. A method of collecting bagworm silk threadsis not limited to a particular method, provided that the bagworm silkthreads are not torn during collection. For example, a scraper or thelike can be used to physically release and collect bagworm silk threadsfrom a rail. Particularly in cases where a rail has a smooth surface ora surface coated with a releasing agent in advance before the spinningprocess, the releasing operation is easily accomplished. By this method,bagworm silk spun fibers running nearly parallel to a rail can becollected.

Additionally, in cases where a rail has a rough surface or a very unevensurface, bagworm silk threads are strongly adhered to the rail by meansof the sericin-like gummy material, which makes it difficult to releaseor collect the silk threads from the rail. In this case, this processand the scouring process as described below may be conductedsimultaneously to prevent bagworm silk threads from being torn duringcollection. According to this procedure, bagworm silk threads can beeasily collected from a rail because the gummy material is degraded andremoved through the scouring process. Additionally, the bagworm silkthreads can be obtained as monofibers without the gummy material, whichare the same as those obtained after the scouring process, because thecollection process and the scouring process are performedsimultaneously. By this process, bagworm foothold silk threads having alength of 1 m or longer can be obtained, which have not hitherto beenphysically obtained.

(3) Scouring Process (S403)

The “scouring process” is a process of scouring long silk threads. Theterm “scouring” refers to removing a sericin-like gummy material fromspun silk threads (spun fibers) to obtain monofibers. This process istypically conducted after the above-described collection process, andmay be conducted simultaneously with the collection process, asdescribed above. Additionally, in cases where a twisting process followsthe collection process, prior to this process, as described below, thisprocess may be conducted after the twisting process. This process is anoptional process and may be conducted as necessary.

A method of scouring bagworm silk threads is not limited to a particularmethod, provided that a gummy material can be removed without weakeningthe strength of the fiber components of the silk threads. For example,any scouring method for silkworm silk threads may be applied.Specifically, bagworm silk threads recovered in the collection processshould be boiled in a sodium bicarbonate solution at a concentration of0.01 mol/L to 0.1 mol/L, 0.03 to 0.08 mol/L, or 0.04 to 0.06 mol/L for atime period from 5 minutes to 1 hour, preferably 10 to 40 minutes, morepreferably 15 to 30 minutes. By this process, monofibers from footholdsilk threads having a length of 1 m or longer can be obtained.

(4) Twisting Process (S404)

The “twisting process” is a process of twisting bagworm silk threadsobtained after the collection process or the scouring process. The term“twisting” refers to winding threads together to produce a yarn. In thisprocess, plural bagworm silk spun fibers and/or monofibers are twistedto produce bagworm silk yarns having toughness.

In the twisting process, monofibers from bagworm silk threads obtainedafter the scouring process may be gathered into bundles and thentwisted, or alternatively bagworm silk spun fibers obtained after thecollection process may be gathered into bundles and then twisted. In theformer case, twisted bagworm silk yarns without a gummy material areobtained. In the latter case, twisted bagworm silk yarns consisting ofspun fibers containing a gummy material are obtained. Thus, the obtainedbagworm silk yarns may be used as bagworm silk yarns which have notundergone the scouring process and consequently contain a gummysubstance, or may be scoured as necessary to produce twisted bagwormsilk yarns without a gummy material.

In this process, bagworm silk fibers may be blended with other fibers,for example animal fibers such as silkworm silk fibers, plant fiberssuch as cotton fibers, synthetic fibers such as polyester fibers, orrecycled fibers such as rayon, or the like, to form bundles of fibersand then to twist the resulting fiber bundles. In the production of onestrand of twisted bagworm silk yarn, the number of constituent spunfibers and/or monofibers is not limited to a particular number. Forexample, the number ranges from 2 to 200, from 4 to 150, from 6 to 100,from 8 to 50, or from 10 to 30.

The twisting is not limited by a particular method. Any methods known inthe art may be implemented. Examples of the method include right-laid(S-laid) and left-laid (Z-laid). The twist number may be determined asappropriate. Plural strands of twisted bagworm silk yarn may be furthertwisted together by the process called plying to produce a thickerbagworm silk yarn. The twisting operation may be performed by hand or byusing a yarn twister.

Long bagworm silk threads, which are obtained by the production methodof the present invention, can be spun together into longer bagworm silkyarns.

2-3. Effect

Long bagworm silk threads having a length of 1 m or longer as monofibersor fiber assemblies, which has hitherto been considered impossible toproduce, can be produced through the above-described processes.Therefore, fabrics comprising bagworm foothold silk threads, which hashitherto been impossible to produce, can also be produced using the longbagworm silk threads according to the present invention as a solematerial or in combination with other fibers. Fabrics made of bagwormsilk threads are beautiful and smooth, and have excellent tensilestrength. Thus, long bagworm silk threads are promising not only as amaterial for clothes but also as a special material for, for example,medical materials and protective clothes, as in the case of spiderthread. Long bagworm silk threads can further be used for quality fabricproducts (for example, quality legless chairs, sofas, curtains, fabricwallpapers, and the like, to which strong friction force is oftenapplied).

According to the method of producing long bagworm silk thread of thepresent invention, pure and long bagworm-derived foothold silk threadshaving a length of 1 m or longer, which contain no contaminants, such aspieces of leaves and twigs, can be churned out.

3. Apparatus for Producing Long Bagworm Silk Thread 3-1. Overview

The third aspect of the present invention is an apparatus for producinglong bagworm silk thread. The production apparatus of the presentinvention is characterized by comprising, as an essential component, arail having a specific width and being capable of holding the legs of abagworm. Long foothold silk threads can be easily obtained from bagwormswith the production apparatus of the present invention.

3-2. Configuration

The production apparatus of the present invention comprises a rail as anessential component. The rail will be described below.

The term “rail” as used herein refers to a path with a linear structureon which a bagworm moves. The “linear structure” as used herein refersto a single-rail structure having a same or substantially same width,whose cross-sectional shape is not limited to a particular shape butincludes circular shapes, approximately circular shapes (including ovalshapes), polygonal shapes (including square and approximately squareshapes), and combinations thereof.

The length of the rail is not limited. Because a bagworm spins afoothold silk thread in the direction along a rail, a longer rail can beused to obtain a longer foothold silk thread in principle. However, themethod according to the first aspect of the present invention cancollect foothold silk threads which have been spun so as to overlap eachother on a rail, so that a foothold silk thread having a length longerthan that of the rail can also be obtained when a bagworm repeatedlytravels along the rail. For example, the rail should have a closed-ringstructure or an open-ring structure with a gap(s) which a bagworm usedcan cross. In this case, a bagworm moves around the circular rail, andthereby a long silk thread can be obtained even if the rail has only alimited length. In this respect, the “closed-ring structure” or the“open-ring structure” has any of circular, approximately circular,square shapes, approximately square, and polygonal shapes, or acombination thereof.

Herein, the rail is not merely a supporting member on which a bagwormholds its legs to bear its own weight, but also the structure and widthof the rail are important to achieve the object of the productionapparatus of the present invention. That is, a rail in the productionapparatus of the present invention is configured to meet the followingthree conditions.

The first condition is related to the linear structure. When a path onwhich a bagworm moves has a linear structure, the moving freely in thelateral direction of a bagworm is restricted, and thereby the bagwormonly allows to move in the direction along the rail in principle. Themovement of a bagworm can be controlled to some extent by the structureof the rail.

The second condition is that the width of a rail is less than themaximum width between the extended legs of a bagworm used to theproduction apparatus of the present invention.

The “width of a rail” as used herein refers to the length of a moiety ofdirectly involved in holding legs. This length generally corresponds tothe transverse (short axis) length of the rail. The maximum width of arail is less than the maximum width between the extended legs of abagworm used to the production apparatus of the present invention. Incontrast, the minimum width of a rail is not limited to a particularlength, as long as a bagworm can hold the legs on the rail. For example,the rail may be on the edge of a thin metal plate with a thickness ofaround 0.5 mm. In the rail shown in FIG. 5A, the cross-sectionaldiameter (φ) corresponds to the width of the rail.

The “maximum width between the extended legs of a bagworm” as usedherein corresponds to the width (W1 or W2) between the left and rightlegs of the bagworm, which are extended as much as possible, as shown inFIG. 5B. A bagworm has three pairs of left and right legs (front legs,middle legs, and rear legs), and the maximum width between the extendedlegs preferably represents either of those except for the longest(maximum) width between the extended legs, namely the second longestwidth or the shortest width between the extended legs, more preferablyrepresents the shortest (minimum) width between the extended legs. InFIG. 5B, the maximum width between the extended middle legs (ML), W1, isthe longest among the three pairs of legs and the maximum width betweenthe extended posterior legs, W2, is the shortest among the three pairsof legs. Therefore, when the width of a rail is determined, the maximumwidth between the extended front legs or between the extended rear legs,particularly the maximum width between the extended posterior legs, W2is preferable as the maximum width between the extended legs of abagworm. The maximum width between extended legs varies depending on thespecies, male and female, and instar of larvae, but generally fallswithin a specific range if the bagworms are the same species of nearlythe same instar. For example, in Eumeta japonica, the maximum widthbetween extended legs of young instar larva (around the first to thirdinstar) ranges from 2 mm to 4 mm or from 3 mm to 5 mm. That of themiddle instar larva (around the fourth to fifth instar) ranges from 3 mmto 7 mm or from 4 mm to 8 mm. That of the penultimate instar larva orlast instar larva ranges from 4 mm to 9 mm, from 5 mm to 10 mm, or from6 mm to 12 mm. In Eumeta minuscula, the maximum width between extendedlegs of young instar larva (around the first to third instar) rangesfrom 1.5 mm to 3.5 mm. That of the middle instar larva (around thefourth to fifth instar) ranges from 2.5 mm to 6 mm or from 3 mm to 7 mm.That of the penultimate instar larva or last instar larva ranges from3.5 mm to 8 mm, from 4 mm to 9 mm, or from 5 mm to 10 mm. Thus, thewidth of a rail should be changed as appropriate according to thespecies, instar, and male and female of bagworms used. In each larvalinstar, the width of a rail is preferably less than the shortest(minimum) among the maximum widths between the extended legs of bagwormsof the species used, in terms of holding legs as described below.

Additionally, the third condition is that a bagworm can hold its legs ona rail.

Specific examples of the manner in which a bagworm “holds its legs on arail” include a manner in which the bagworm holds the rail with at leasta pair of legs, one each from the left and right sides, among the threepairs of legs, for a total of six legs. For example, FIG. 6A shows apicture taken from above a rail (arrow) made of a metal wire. In FIG.6A, a bagworm moves in the direction indicated by the thick arrow byholding the rail between the six legs (arrowheads) from underneath. Inthis case, the bagworm is hung down from the rail. In thisspecification, the rail floor is directed downward when a bagworm hangsdown from the rail as shown in the picture. In FIG. 6A, the rail flooris a surface facing the venter of the bagworm, which is out of sight inthe picture.

Additionally, a manner in which a bagworm hooks the legs on either theleft or right side on a rail from above is given as another example. Forexample, FIG. 6B shows a picture taken diagonally above a rail (arrow)located on the edge of a metal plate. In FIG. 6B, a bagworm moves in thedirection indicated by the thick arrow by hooking the three right legs(arrowheads) onto the rail. In this case, a bagworm hangs down from aside surface of the rail by hooking the legs on the rail. Herein, therail floor is directed upward when a bagworm hangs down from a sidesurface of the rail, as shown in the picture. In FIG. 6B, the rail flooris a surface on which the legs of a bagworm are hung.

Any rail which fails to hold a bagworm is considered as not meeting therequirements for the rail of the present invention, even if the rail hasa width less than the maximum width between the extended legs of thebagworm used to the production apparatus of the present invention. Forexample, in cases where the edge of a plate member made from a materialwith a smooth surface is configured into a rail, A to F shown in FIG. 7are illustrated as the example. As a prerequisite, the width of a railaccording to any of A to F shall be less than the maximum width betweenthe extended legs of a bagworm. Among those, each of A to C shows a railfloor directed upward. In A, no bump is formed between the plate memberand the edge (rail: 701); in B, the thickness of the rail is increasedrelative to that of the plate member on both sides to form an expandedportion; and in C, the thickness of the rail is increased relative tothat of the plate member on only one side to form an expanded portion.In any configuration, a bagworm can hang on the rail. In contrast, eachof D to F shows a rail floor directed downward. The rails according to Dto F have similar structures according to A to C, respectively. Amongthose, each of E and F includes an expanded portion formed on a rail,which assists a bagworm to hang on to the rail, and D includes no bumpfunctioning as a foothold on a rail, which no longer allows a bagworm tohang on the rail. Thus, any configuration as shown by D does not meetthe requirements for the rail that is capable of holding the legs of abagworm.

The material of the rail is not limited. For example, metals, ceramics(including enamel), glass, stones, resins (including synthetic andnatural resins), wood materials (including branch, vine, bamboo, and thelike), fibers, bones and fangs, and combinations thereof can be used.The material preferably has a sufficient strength to be invulnerable tobiting attack of bagworms. For example, metals, ceramics, glass, stones,and the like are suitable. Additionally, a portion of a rail to whichbagworm silk threads are adhered is preferably made from a material witha smooth surface to facilitate collection of bagworm spun silk threads.The “material with a smooth surface” as used herein refers to a materialprocessable to form a smooth surface, such as metals, glass, andplastics. Additionally, any material coated with a paint or the like toobtain a smooth surface is included in the material with a smoothsurface, even if the original material is difficult to polish for theformation of a smooth surface, such as wood materials and fibers.

The form of a member including a rail (a rail member) is not limited.For example, the rail member may have a wire-like or string-likestructure like a metal wire which per se forms a rail, or may have aplate structure. In cases where the rail member is a plate member, arail is included on the edge of the plate member. In this respect, theplate member and the edge may be made from an identical material or fromdifferent materials.

Embodiments of the rail will be described by illustrative examples shownin FIGS. 8 to 10 . FIG. 8 depicts an example of the rail configured asthe edge of a plate member (801). The rail (802) in this drawing has aclosed-ring structure with the rail floor directed upward. A bagworm(803) placed on the rail in this production apparatus principallycontinues to move in the direction indicated by the arrow. FIG. 9depicts an example of the rail which is made of a wire member such as ametal wire. The rail (901) in this drawing has a helical structure.Because bagworms have a tendency to move to a higher location, a bagworm(902) placed on the lower end of the rail in this apparatus movesupward, while spinning a thread. Once the bagworm reaches the upper endof the helical rail, the apparatus is turned upside down and the bagwormis again positioned at the lower end of the wire member, which allowsthe bagworm to continue continuous spinning. Additionally, FIG. 10depicts an example of the rail which comprises a combination of circularrails and a linear rail. In FIG. 10 , two closed ring-like rails (1001,1002) are connected to one linear rail (1003), wherein those rails aremade of a wire member such as a metal wire. A bagworm (1004) continue tomove in the direction indicated by the arrow and then to return on thelinear rail and/or move around the circular rail in the apparatus.

The rail in the production apparatus of the present invention may have aslope. The slope relative to the horizontal surface preferably rangesfrom 0 to 70 degrees or from 0 to 50 degrees upward, or ranges from 0 to70 degrees or from 0 to 50 degrees downward. The term “upward” or“downward” refers to the angle of the rail floor. For example, in caseswhere the production apparatus of the present invention comprises a railon the edge of a plate member, as shown in FIG. 11 , and the rail flooris directed upward, as shown in FIG. 11A, the inclination angle (a)between the horizontal surface and the rail floor should range from 0 to70 degrees. Additionally, in cases where the rail floor is directeddownward, as shown in FIG. 11B, the inclination angle (b) between thehorizontal surface and the rail floor should range from 0 to 70 degrees.

3-3. Effect

According to the production apparatus for long bagworm silk thread, themethod for producing long bagworm silk thread according to the presentinvention can readily be implemented, and the production of long bagwormfoothold silk threads having a length of 1 m or longer can easily beobtained by using the production apparatus, which has hitherto beenimpossible.

EXAMPLES Example 1: Production of Long Bagworm Silk Threads (Purpose)

Bagworm foothold silk threads are produced by the method according tothe present invention for producing long bagworm silk thread.

(Method)

As the bagworm, the last instar larvae of Eumeta japonica collected atan orchard in Tsukuba, Ibaraki, Japan t were used (n=50). A productionapparatus according to the present invention for long bagworm silkthread was used to produce long bagworm silk threads. An approximatelysquare metal can was used as the production apparatus. In the metal can,a closed ring-like rail with its floor directed upward, which has awidth of 1.7 mm and a perimeter of 1.1 m, is on the upper edge of theplate member corresponding to the side surface of the metal can. Onebagworm was placed on the inner bottom surface of the metal can. Afterobserving the state that the bagworm was reached the rail and movearound the rail with spinning of threads, the bagworm was left on therail directly for two days (i.e., the spinning process). Two days later,the bagworm was recovered or removed from the apparatus and bagworm silkthreads (foothold silk threads) overlapped with each other on the railwere removed by using a scraper to collect an approximately squarering-shaped a bundle of bagworm silk threads (silk bundle) (i.e., thecollection process). The total length of the spun foothold silk threadswas calculated from the number of spun fibers constituting the obtainedsilk bundle and the perimeter of the rail. Then, any gummy materialadhered to bagworm silk threads was scoured. In the scouring conditions,the bagworm silk threads were boiled in a 0.05 mol/L aqueous solution ofsodium carbonate for 15 minutes, and further boiled for another 15minutes after the aqueous sodium carbonate solution was replaced withfresh aqueous solution (i.e., the scouring process). After the scouringprocess for a total of 30 minutes, the bagworm silk threads werethoroughly washed with pure water and then dried in air. The 150 or morebagworm silk threads (monofibers) obtained after the scouring processwere twisted by hand into bagworm silk yarns (i.e., the twistingprocess). The bagworm silk yarns were used in warp and weft to weave afabric made of bagworm silk.

(Result)

The bagworm, which had been placed on the inner bottom surface of thecontainer, then spontaneously climbed to the wall until the bagwormreached the closed ring-like rail located on the top of the wall, andsubsequently continued to move in the same direction around the railwith continuous spinning of threads. The time required for the bagwormto move once around the 1.1 m rail with spinning of threads was fromabout 5 minutes 30 seconds to about 7 minutes 30 seconds. This resultindicated that the last instar larvae of Eumeta japonica can spin athread at around a rate of 150 to 200 mm/min (1100 mm/7.5 min to 1100mm/5.5 min), which is equal to about half the spinning rate of silkworms(300 to 400 mm/min; Kei-ichi Komatsu, 1997, “Invitation to Silk”,Sciencehouse Inc., p 20).

FIG. 12 shows bundles of bagworm silk threads obtained after thecollection process and wound around a bobbin (a) or handles of paintbrushes (b and c). Though it was difficult to collect spun fibers ofnest silk threads even as short as 50 cm in accordance with conventionaltechniques, the method according to the present invention for producinglong bagworm silk thread allowed bagworms to produce longer footholdsilk threads.

FIG. 13A depicts a view under a stereoscopic microscope of a bundle ofbagworm silk threads obtained after the collection process. The bagwormfoothold silk threads in this view were observed to run nearly parallelin the same direction and not to complicatedly tangle with each other.Additionally, the silk bundle in the view is a bundle of silk threadsreleased and collected from the rail after the collection process. Itwas difficult to count the exact number of spun fibers in the silkbundle. However, the silk bundle was estimated to consist of at least150 spun fibers. This result indicates that the bagworm moved at least150 times around the closed ring-like rail with spinning of threads,which means that bagworm foothold silk threads with a length of at least165 m (1.1 m×150) or longer in total were produced by the methodaccording to the present invention for producing long bagworm silkthread because the rail was 1.1 m long in total. Considering the factthat it was almost impossible to stably obtain bagworm silk threads with1 m or longer in accordance with conventional techniques, this resulthas demonstrated a significant effect of the method according to thepresent invention for long bagworm silk thread production. Much longerbagworm silk threads can be obtained by making bagworms spin threads fora longer period of time under optimized conditions.

Additionally, the bagworm silk threads obtained in this procedure arefoothold silk threads collected from a rail made of a metal andtherefore are pure bagworm silk threads completely without any pieces ofleaves and twigs. The bagworm silk threads obtained in this procedureare slightly fuzzy because a sericin-like gummy material remains on thesilk.

FIG. 13B depicts a view under a stereoscopic microscope of a bundle ofbagworm silk threads obtained after the scouring process. It wasobserved that the gummy material and fuzz were completely removed by thescouring process, and thereby the bagworm silk became only monofibers.

FIG. 13C depicts a view of a bagworm silk yarn obtained after thetwisting process. It was observed that bagworm silk yarns as shiny andtough as ordinary silkworm silk yarns were obtained by the twistingprocess.

FIG. 13D depicts an enlarged view of a woven fabric produced by weavingthe twisted bagworm silk yarns. It was demonstrated that the methodaccording to the present invention for producing long bagworm silkthread enables production of a woven fabric using bagworm silk yarns,which has hitherto been impossible.

Example 2: Examination of Continuous Spinning Behavior of Bagworms(Purpose)

Bagworms have a tendency to spin foothold silk threads at least duringmigration. Accordingly, a bagworm continuously spins a thread as long asthe bagworm continues to move on a rail, which also corresponds to thelength of bagworm silk monofibers obtained by the present invention.Thus, the inventors examined how many hours bagworms can continue tospin on the apparatus according to the present invention for producinglong bagworm silk thread.

(Method)

As the bagworm, the last instar larvae of Eumeta minuscula collectedfrom trees planted in the grounds of National Agriculture and FoodResearch Organization, Japan were used (n=8). A stainless dish having adiameter (φ) of 75 mm and comprising a closed ring-like rail, which hasa width of 0.85 mm and a perimeter of 235 mm, was used as the productionapparatus. After one bagworm was placed on the bottom surface of thestainless dish, the time required for the bagworm to move from the startpoint to the end point of the rail was measured.

(Result)

The measured time of continuous spinning and length of spun fiber arepresented in Table 1.

TABLE 1 1 2 3 4 5 6 7 8 Average Time of continuous  51  51  50  48  48 38  34  34  44.25 spinning (hr) Length of spun fiber 459 459 450 432432 342 306 306 398.25 (m)

It was found that the Eumeta minuscula continued to spin foothold silkthreads while moving on the rail for 34 to 51 hours withoutinterruption. That is, it was indicated that the use of the apparatusaccording to the present invention for producing long bagworm silkthread allows the bagworms to continuously spin threads from about 1.5days to about two days without needing any special conditions oroperations and also without eating or resting.

After the spinning process, a bundle of silk threads running nearlyparallel to the rail was collected from the rail, similarly toExample 1. The total length of bagworm silk threads was calculated to befrom 306 m to 459 m, based on the perimeter of the rail in theproduction apparatus.

From the time required to move once around the rail on the stainlessdish, it was indicated that the last instar larvae of Eumeta minusculacan spin threads at almost the same rate as the last instar larvae ofEumeta japonica.

Example 3: Examination of Mechanical Properties of Bagworm Silk Threads(Purpose)

The mechanical properties of bagworm silk threads were examined.

(Method)

Spun fibers (bifilaments) obtained before scouring were used as thebagworm silk threads. A portion of the spun fibers obtained after thecollection process in Example 1 were used as foothold silk threads(n=9). Additionally, silk threads collected from the innermost layers ofnests for the last instar larvae of Eumeta japonica were used as nestsilk threads (n=5). After dissecting the Eumeta japonica nests, thesamples having a length of about 30 mm from the surface of the innermostlayers were manually collected.

A tensile test was performed on each type of bagworm silk threads toevaluate four different mechanical properties: initial elastic modulus,fracture strength, elongation at break, and toughness. The initialelastic modulus refers to a value given as the initial slope of astress-strain curve, which corresponds to the proportional constant inthe deformation area meeting Hooke's law, which is the proportionalrelationship between stress and strain when a sample is pulled. Ingeneral, a higher value of the initial elastic modulus means a smallerstrain for a given tensile stress, meaning more stiffness. Additionally,the fracture strength refers to the maximum stress applied to a threadjust before the thread breaks. In general, a higher value of theultimate tensile strength means a higher degree of resistance to stress.Furthermore, the elongation at break refers to the increased length of athread at its break point. In general, a higher value of the elongationat break means a higher elasticity. Moreover, the toughness refers tothe amount of work (energy) required to fracture a thread, which isgiven as the area under the stress-strain curve. In general, a highervalue of the toughness means a higher degree of resistance to fracture.

The measurements were performed using a load cell of 5 N on a tensiletester (EZ Test; Shimadzu Co.) under the following measurementconditions: gauge length (the initial length of a sample), 13 mm;tensile speed, 10 mm/min; measurement environment, room temperature (25°C.) and 30% of humidity.

To evaluate the above-described four properties, a stress-strain curvewas prepared by converting each measured value in the tensile test to astress value obtained by dividing measured value by the cross-sectionalarea of each monofiber in the bagworm silk threads. The cross-sectionalarea of a monofiber was calculated as follows. When foothold and nestsilk threads spun by a bagworm are observed under a scanning electronmicroscope (SEM), either of them shows a structure consisting of twoflattened monofibers (monofilaments), as shown in FIG. 3 , joinedside-by-side along the longitudinal axis of each fiber by a gummymaterial. As shown in FIG. 3B, the cross section of a monofiber has anelliptical shape. When the ratio (a/b) between the major axis (a) andminor axis (b) of the ellipse was calculated, the ratio was led to thefollowing value in either case of the foothold and nest silk threads:a/b=1.67±0.12 (n=15). The elliptical major axis (a) of two monofibersconstituting the bagworm silk thread were measured used a lightmicroscope (BZ-X700; KEYENCE Co.) for each sample used, and thecross-sectional area of each monofiber was calculated according to theelliptical area formula (A=πab), based on the assumption that eachmonofiber has a cross section with the ratio a/b=1.67.

(Result)

The calculated values of the mechanical properties are presented inTable 2. In this table, the values of the same mechanical properties ofbagworm silk threads from Eumeta minuscula, silkworm silk threads fromBombyx mori, and spider threads from Araneus ventricosus are shown ascontrols, which are cited from references. The methods to calculate themechanical properties of the controls are the same as those for themechanical properties of the present embodiment.

TABLE 2 Elastic Fracture strength Elongation at Toughness modulus (GPa)(GPa) break (%) (MJ/m³) Eumeta Foothold 33.04 (±3.52) 2.02 (±0.33) 24.67(±4.41) 282.23 (±49.90) japonica silk thread Nest silk 18.17 (±4.53)1.46 (±0.19) 27.40 (±3.23) 238.27 (±28.12) thread Silk thread 27.09(±3.21) 1.80 (±0.22) 25.76 (±2.88) 264.64 (±31.86) average Eumetaminuscula*¹ 25 — — — Bombyx mori*²  7 0.6 18  70 Araneus ventricosus*²10 1.1 27 160 (References) *¹Shigeyosi Ohsaki, 2002, Sen'i Gakkaishi(Sen'i To Kogyo), 58: 74-78. *²Gosline J. M., et al., 1999, 202,3295-3303.

It was found that bagworm silk threads from Eumeta japonica included atleast two types of silk threads, namely foothold and nest silk threads,showing different mechanical properties, as shown in Table 1.Additionally, it was found that the values of mechanical propertiesincluding initial elastic modulus, fracture strength, and toughness werehigher in the foothold silk threads than in the nest silk threads.

In contrast, bagworm silk threads, particularly foothold silk threads,from Eumeta japonica had quite excellent mechanical properties, comparedwith silkworm silk threads from Bombyx mori and spider threads fromAraneus ventricosus. For example, the elastic modulus of the footholdsilk threads from Eumeta japonica bagworms was about 5 times higher thanthat of the silkworm silk threads and 3 times or more higher than thatof the spider threads; the fracture strength of the foothold silkthreads was 3 times or more higher than that of the silkworm silkthreads and about 2 times higher than that of the spider threads; andthe toughness of the foothold silk threads was 4 times or more higherthan that of the silkworm silk threads and 1.7 times or more higher thanthat of the spider threads. Additionally, the elongation at break of thefoothold silk threads was 1.3 times or more higher than that of thesilkworm silk threads and was nearly equal to that of the spiderthreads.

All publications, patents, and patent applications cited herein shouldbe incorporated herein by reference in their entirety.

1. A bagworm-derived silk thread having a continuous length of 1 meteror longer.
 2. A fabric comprising a silk thread according to claim 1.